1
00:00:00,470 --> 00:00:00,770
Now.

2
00:00:00,770 --> 00:00:09,050
Previously, before cider was used, we had class full address masks, so we had class addresses, class

3
00:00:09,050 --> 00:00:11,930
B addresses and class C addresses.

4
00:00:12,140 --> 00:00:18,250
A Class A subnet supports about 16 million addresses and uses the mosque.

5
00:00:18,260 --> 00:00:20,960
255.0.0.0.

6
00:00:20,990 --> 00:00:30,080
Class P networks support about 65,000 host addresses with a mask of 255.255.00.

7
00:00:30,350 --> 00:00:39,230
Class C Networks support 254 host addresses and use a mask of 255225 5 to 55.0.

8
00:00:39,500 --> 00:00:47,430
The problem with this method is what happens if a company wants to support 3000 hosts, for example?

9
00:00:47,450 --> 00:00:54,470
So if the network had 3000 hosts, which of these three address classes with the company get?

10
00:00:54,620 --> 00:01:00,140
Well, they could get a class B address, but that's an awful waste of a lot of addresses.

11
00:01:00,410 --> 00:01:05,540
About 65,000 addresses are available in a Class B subnet.

12
00:01:05,690 --> 00:01:11,240
But in this example, the company only needs 3000 host addresses.

13
00:01:11,660 --> 00:01:18,920
They could get multiple class C networks, but that means that they're going to be allocated many Class

14
00:01:18,920 --> 00:01:23,510
C addresses, which has a negative effect on Internet routing tables.

15
00:01:23,930 --> 00:01:32,050
Now, rather than doing that, we can move the subnet mask insider notice in Class A, B and C addresses.

16
00:01:32,060 --> 00:01:40,010
The subnet mask is set on the octet boundary notice in class A, B and C addresses the subnet mask is

17
00:01:40,010 --> 00:01:44,810
set on the octet boundary plus a first eight bits.

18
00:01:45,080 --> 00:01:47,600
Class B First 16 bits.

19
00:01:47,690 --> 00:01:50,540
Class C first 24 bits.

20
00:01:50,660 --> 00:01:56,640
But rather than doing that with CIDR, the subnet mask can be somewhere in the middle.

21
00:01:56,660 --> 00:02:00,200
It doesn't have to be on the octet boundary.

22
00:02:00,660 --> 00:02:02,180
Here's another example.

23
00:02:02,390 --> 00:02:11,060
In this example, we've got a subnet mask of 255.224.0.0245.

24
00:02:11,060 --> 00:02:13,780
In binary is eight binary ones.

25
00:02:13,790 --> 00:02:19,090
2 to 4 is three binary ones, followed by five binary zeros.

26
00:02:19,100 --> 00:02:23,260
So if we count the number of binary ones, that gives us 11.

27
00:02:23,270 --> 00:02:30,620
So 250 52240.0 is the same as slash 11.

28
00:02:31,040 --> 00:02:36,910
The network portion is on the left hand side, the host portion is on the right hand side.

29
00:02:36,920 --> 00:02:45,140
But notice once again that the divider between network and host is not on the octet boundary, it's

30
00:02:45,140 --> 00:02:47,330
somewhere within the octet.

31
00:02:47,540 --> 00:02:54,740
So in this example, the most significant three bits of that octet are network and the remaining portion

32
00:02:54,740 --> 00:02:56,750
of the octet is host.

33
00:02:56,930 --> 00:03:01,010
Now in the subnet videos, I'm going to show you this in a lot more detail.

34
00:03:01,010 --> 00:03:03,200
We're going to work out various types of subnets.

35
00:03:03,710 --> 00:03:11,270
What I need you to understand with regards to CIDR at this point is that CIDR allows us to implement

36
00:03:11,270 --> 00:03:13,580
a variable length subnet masks.

37
00:03:13,850 --> 00:03:22,970
No longer do we have class A, B and C networks where class A is always slash eight, class B is always

38
00:03:22,970 --> 00:03:28,130
slash 16, and class C is always slash 24.

39
00:03:28,370 --> 00:03:34,370
When CIDR is used, the mosque's can vary and that's what we use today.

40
00:03:34,760 --> 00:03:41,330
So from 1993, CIDR is more preferable than class full network masks.

41
00:03:41,420 --> 00:03:48,200
Now, once again in the subheading videos, I'm going to discuss subnets in a lot more detail, so please

42
00:03:48,200 --> 00:03:55,040
refer to those videos if you want to learn more about how to subnet a network or how to work out the

43
00:03:55,040 --> 00:04:02,360
maximum hosts that can be supported on a subnet, or which addresses the first address or last address,

44
00:04:02,360 --> 00:04:06,980
or what is the broadcast address and so forth for a specific subnet.